1. Field of the Invention
The present invention relates to a magnetic detection device used primarily with a hard disk drive, a magnetic sensor, or the like. More particularly, the invention relates to a magnetic detection device that permits proper control of the magnetization of a free magnetic layer even in a design with narrower tracks, and exhibits excellent reproducing characteristics, and a manufacturing method for the same.
2. Description of the Related Art
FIG. 35 is a partial sectional view of the structure of a conventional magnetic detection device observed from a surface opposing a recording medium.
In FIG. 35, a multilayer film 8 formed on a substrate 1 includes an antiferromagnetic layer 2, a pinned magnetic layer 3, a nonmagnetic material layer 4, and a free magnetic layer 5. Hard bias layers 6 are formed on both sides of the multilayer film 8, and electrode layers 7 are formed on the hard bias layers 6.
The magnetization of the pinned magnetic layer 3 is fixed in a direction Y in the drawing by an exchange coupling magnetic field generated between itself and the antiferromagnetic layer 2. On the other hand, the magnetization of the free magnetic layer 5 is pinned in a direction X in the drawing by a longitudinal bias magnetic field from the hard bias layer 6.
As shown in FIG. 35, a track width Tw is restricted by the width dimension in the direction of the track width (in the direction X in the drawing) of the free magnetic layer 5. With a higher recording density in the future, the dimension of the track width Tw will be further reduced.
The tracks that are becoming increasingly narrower have been preventing the structure of the magnetic detection device shown in FIG. 35 from properly controlling the magnetization of the free magnetic layer 5.
First, according to the structure illustrated in FIG. 35, as the width dimension of the free magnetic layer 5 is reduced to accommodate narrower tracks, the region subjected to the influences of an intense longitudinal bias magnetic field from the hard bias layer 6 takes up more percentage in the free magnetic layer 5. The area affected by the intense longitudinal bias magnetic field turns into a dead region that is magnetically less responsive to an external magnetic field. With narrower tracks, the dead region grows larger, resulting in degraded reproduction sensitivity.
Second, the hard bias layer 6 and the free magnetic layer 5 are apt to develop magnetic discontinuity. This trend is especially true if a foundation layer formed of Cr or the like lies between the hard bias layer 6 and the free magnetic layer 5.
Such magnetic discontinuity causes enhanced influences of the diamagnetic fields of the end portions of the free magnetic layer 5 in the width direction, frequently leading to a phenomenon known as the xe2x80x9cbuckling phenomenonxe2x80x9d in which the magnetization of the free magnetic layer 5 is disturbed. The buckling phenomenon tends to take place in a wider region of the free magnetic layer 5 as the tracks become narrower. This reduces the stability of the reproduced waveforms.
Third, with a narrower gap, a part of the longitudinal bias magnetic field from the hard bias layer 6 escapes to a shielding layers (not shown) formed on the top and bottom of the magnetic detection device shown in FIG. 35. This disturbs the magnetization of the shielding layers and weakens the longitudinal bias magnetic field to be supplied to the free magnetic layer 5, preventing effective control of the magnetization of the free magnetic layer 5.
To overcome the problem described above, the exchange bias method has recently been used. According to the method, the magnetization control of the free magnetic layer 5 is attained using an antiferromagnetic layer formed on the free magnetic layer.
The magnetic detection device using the exchange bias method is fabricated according to the manufacturing process illustrated in, for example, FIG. 36 and FIG. 37, which are partial sectional views of the magnetic detection device observed from its surface opposing a recording medium.
In the process illustrated in FIG. 36, the antiferromagnetic layer 2 made of, for example, a PtMn alloy is formed on the substrate 1. Then, the pinned magnetic layer 3, the nonmagnetic material layer 4, and the free magnetic layer 5 made of a magnetic material are deposited thereon. A Ta film 9 is formed on the free magnetic layer 5 to prevent the latter from being oxidized when its surface is exposed to the atmosphere.
Subsequently, a liftoff resist layer 10 is formed on the Ta film 9 shown in FIG. 36. The portion of the Ta film 9 exposed on both sides in the track width direction or the direction X in the drawing that is not covered by the resist layer 10 is then completely removed by ion milling. The free magnetic layer 5 under the Ta film 9 is also partly removed, as indicated by the dotted lines in the drawing.
In the step illustrated in FIG. 37, ferromagnetic layers 11, second antiferromagnetic layers 12 formed of an IrMn alloy or the like, and electrode layers 13 are deposited in this order on the portions of the free magnetic layers 5 that are exposed on both sides of the resist layer 10. Removing the resist layer 10 shown in FIG. 37 completes the exchange bias type magnetic detection device.
In the magnetic detection device shown in FIG. 37, the track width Tw can be restricted in terms of the interval in the track width direction (in the direction X in the drawing) of the ferromagnetic layers 11. The ferromagnetic layers 11 are firmly fixed by the exchange coupling magnetic field generated between themselves and the second antiferromagnetic layers 12. This causes both ends A of the free magnetic layers 5, which are positioned under the ferromagnetic layers 11, to be firmly fixed in the direction X in the drawing by the ferromagnetic coupling between themselves and the ferromagnetic layers 11. Thus, it has been believed that a central portion B of the free magnetic layer 5 in the area of the track width Tw is formed into a weak single domain so it is able to magnetically respond to an external magnetic field.
The use of an exchange bias type magnetic detection device has been expected to provide a solution to the problems described above.
However, the magnetic detection device formed according to the manufacturing process illustrated in FIG. 36 and FIG. 37 poses the following shortcomings.
First, during the ion milling step in the process illustrated in FIG. 36, a part of the free magnetic layer 5 formed under the Ta film 9 is inevitably removed while removing the Ta film 9. In addition, an inert gas used for ion milling, such as Ar, is apt to enter through the exposed portion of the free magnetic layer 5. The damage caused by the ion milling set forth above tends to destroy the crystal structure of surface portions 5a of the free magnetic layer 5, or to the occurrence of lattice defects (mixing effect). This frequently results in the degradation of the magnetic characteristics of the surface portions 5a of the free magnetic layer 5.
Ideally, only the Ta film 9 is removed in the ion milling step of the process illustrated in FIG. 36, leaving the free magnetic layer 5 intact. In reality, it is difficult to achieve such degree of milling control.
The reason underlying the difficulty in achieving ideal milling control is due to the thickness of the Ta film 9 formed on the free magnetic layer 5. The Ta film 9 is formed to have a thickness in the range of between about 30 angstroms to about 50 angstroms. This film thickness is necessary to adequately protect the free magnetic layer 5 from oxidation.
The Ta film 9 is, however, oxidized by being exposed to air or during annealing in a magnetic field to produce an exchange coupling magnetic field between the pinned magnetic layer 3 or the ferromagnetic layers 11 and the antiferromagnetic layers 2 or 12. The thickness of the oxidized portion increases, causing the entire thickness of the Ta film 9 to increase from that in the initial film forming step. For instance, if the thickness of the Ta film 9 is 30 angstroms upon completion of the film formation, the thickness of the Ta film 9 after oxidation will be about 45 angstroms.
Therefore, it is necessary to use high-energy ion milling to effectively remove the Ta film 9 with its increased thickness due to oxidation. High-energy ion milling means high milling rate. It is almost impossible to stop milling once the thick Ta film 9 has been removed by ion milling. In other words, higher-energy ion milling requires a larger milling stop margin. Thus, a part of the free magnetic layer 5 formed under the Ta film is undesirably removed and the free magnetic layer 5 is subjected to more damage from high-energy ion milling and its magnetic characteristics exhibit more conspicuous deterioration.
Second, it is difficult to stop ion milling in the middle of the free magnetic layer 5 shown in FIG. 36 because of the thinness of the free magnetic layer 5, which ranges between about 30 angstroms to about 40 angstroms. In the worst case, both end portions A of the free magnetic layer 5 is completely removed by ion milling.
Third, the surface of the free magnetic layer 5 exposed by ion milling as described above develops deteriorated magnetic characteristics attributable to the ion milling. This results in inadequate magnetic coupling or ferromagnetic exchange interaction between the free magnetic layer 5 and the ferromagnetic layers 11 deposited thereon. For this reason, the ferromagnetic layers 11 must be thick.
However, as the thickness of the ferromagnetic layers 11 increases, the exchange coupling magnetic field generated between the ferromagnetic layers 11 and the antiferromagnetic layers 12 weakens. Thus, both end portions A of the free magnetic layer 5 cannot be firmly fixed magnetically, and a side-reading problem arises, making it impossible to fabricate a magnetic detection device capable of accommodating narrower tracks.
If the thickness of the ferromagnetic layers 11 is excessively thick, then extra static magnetic field tends to reach a central portion B of the free magnetic layer 5 from the inner side surfaces of the ferromagnetic layers 11. This frequently causes degraded sensitivity to an external magnetic field of the central portion B of the free magnetic layer 5, which permits inverted magnetization.
Thus, a magnetic detection device structure, in which the Ta film 9 is formed on the free magnetic layer 5, and the ferromagnetic layers 11 and the second antiferromagnetic layers 12 are laminated on the portions of the free magnetic layer 5 that have been exposed by removing both end portions of the Ta film 9, has not yet made it possible to properly perform magnetization control of the free magnetic layer 5. Therefore current techniques do not permit manufacture of a magnetic detection device that properly accommodates tracks narrower than those in conventional magnetic detection devices.
It is an object of the invention to provide a magnetic detection device able to effectively control the magnetization of a free magnetic layer using an exchange bias method and to successfully accommodate narrower tracks, and a method for manufacturing the same.
According to a first aspect of the present invention, there is provided a magnetic detection device that includes a multilayer film having a first antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic material layer, and a free magnetic layer, these components being arranged in this order from the bottom,
wherein a second antiferromagnetic layer is provided on the free magnetic layer, a nonmagnetic layer is provided at least on a central portion of the second antiferromagnetic layer, and third antiferromagnetic layers are provided on both end portions of the second antiferromagnetic layer.
In the present invention, the second antiferromagnetic layer is provided on the free magnetic layer, and the third antiferromagnetic layers are provided on both end portions of the second antiferromagnetic layer as set forth above. Hence, the thick antiferromagnetic layers combining the second antiferromagnetic layers and the third antiferromagnetic layers are formed on both end portions of the free magnetic layer. Both end portions of the free magnetic layer are properly fixed along a track width direction by an exchange coupling magnetic field generated between the free magnetic layer and the antiferromagnetic layers. The central portion of the free magnetic layer is formed into a weak single domain that permits inverted magnetization in response to an external magnetic field.
The nonmagnetic layer provided on the central portion of the second antiferromagnetic layer protects the second antiferromagnetic layer from oxidation caused by air exposure. The nonmagnetic layer may be provided between both end portions of the second antiferromagnetic layer and the third antiferromagnetic layers.
In the conventional magnetic detection device shown in FIG. 37, both end portions of the free magnetic layer are partly removed. In the present invention, the free magnetic layer is covered by the second antiferromagnetic layer, thus solving a prior art problem in which the free magnetic layer is damaged by ion milling.
The structure according to the present invention allows more effective control of the magnetization of the free magnetic layer than in a conventional magnetic detection device, making it possible to manufacture magnetic detection devices that can successfully accommodate narrower tracks.
Preferably, when a nonmagnetic layer is provided between both end portions of the second antiferromagnetic layer and the third antiferromagnetic layers, the nonmagnetic layer is thicker at its central portion than at its end portions on both sides.
Preferably, a nonmagnetic layer of 3 angstroms or less is provided between the third antiferromagnetic layers and the second antiferromagnetic layer. Alternatively, the third antiferromagnetic layers are directly formed on both end portions of the second antiferromagnetic layer.
The presence of the nonmagnetic layer of 3 angstroms or less makes it easier for antiferromagnetic interaction to take place between both end portions of the second antiferromagnetic layer and the third antiferromagnetic layers. This causes both end portions of the second antiferromagnetic layer and the third antiferromagnetic layers to act like a combined one-piece antiferromagnetic layer, allowing both end portions of the free magnetic layer to be properly and firmly fixed in the track width direction.
Preferably, the thickness of the nonmagnetic layer formed on the central portion of the second antiferromagnetic layer ranges from 3 angstroms to 10 angstroms.
Preferably, the central portion of the second antiferromagnetic layer exhibits non-antiferromagnetic characteristics, while both end portions of the second antiferromagnetic layer exhibit antiferromagnetic characteristics.
If the central portion of the second antiferromagnetic layer exhibits non-antiferromagnetic characteristics, it would be difficult for the central portion of the second antiferromagnetic layer to develop order transformation even by annealing in a magnetic field. Hence, no exchange coupling magnetic field is generated between the central portion of the second antiferromagnetic layer and the central portion of the free magnetic layer. As a result, the magnetization of the central portion of the free magnetic layer will not be firmly fixed along the track width direction.
The end portions at both sides of the second antiferromagnetic layer and the third antiferromagnetic layers formed thereon are combined into one antiferromagnetic layer, permitting easy order transformation by annealing in a magnetic field. Thus, an exchange coupling magnetic field is produced between both end portions of the second antiferromagnetic layer and both end portions of the free magnetic layer. As a result, both end portions of the free magnetic layer can be firmly fixed along the track width direction.
The thickness of the second antiferromagnetic layer preferably ranges from about 20 angstroms to about 50 angstroms, more preferably from about 30 angstroms to about 40 angstroms. These thickness ranges prevent the occurrence of an exchange coupling magnetic field between the central portion of the second antiferromagnetic layer and the central portion of the free magnetic layer. But even if an exchange coupling magnetic field is generated, its magnitude will be extremely small.
According to a second aspect of the present invention, there is provided a magnetic detection device that includes a multilayer film having a first antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic material layer, and a free magnetic layer, these components being arranged in this order from the bottom,
wherein second antiferromagnetic layers are provided at least on both end portions of the free magnetic layer, nonmagnetic layers are provided on the second antiferromagnetic layers, and third antiferromagnetic layers are provided on the nonmagnetic layers.
Unlike the magnetic detection device according to the first aspect of the present invention, the nonmagnetic layer is always provided between the second antiferromagnetic layers and the third antiferromagnetic layers. The second antiferromagnetic layer may not be provided on a central portion of the free magnetic layer. This structural difference arises from the manufacturing method used.
In this embodiment, the second antiferromagnetic layers and the third antiferromagnetic layers are deposited on both end portions of the free magnetic layer, the second antiferromagnetic layers and the third antiferromagnetic layers acting like a single antiferromagnetic layer. Hence, the magnetization of both end portions of the free magnetic layer are firmly fixed in a track width direction by an exchange coupling magnetic field generated between the free magnetic layer and the second antiferromagnetic layers. The central portion of the free magnetic layer is loosely formed into a single domain that permits magnetic reaction to an external magnetic field.
In the conventional magnetic detection device shown in FIG. 37, both end portions of the free magnetic layer are partly removed. In contrast, in the present invention, the free magnetic layer is covered by the second antiferromagnetic layers, which overcomes a problem in the prior art.
The structure according to the present invention allows more effective control of the magnetization of the free magnetic layer than in the conventional magnetic detection device. Thus, the structure of the present invention makes it possible to manufacture magnetic detection devices that can successfully accommodate tracks narrower than those in conventional magnetic detection devices.
Alternatively, the second antiferromagnetic layer may be provided also on a central portion of the free magnetic layer. Thus, the entire top surface of the free magnetic layer is covered by the second antiferromagnetic layer, so the free magnetic layer is protected from ion milling.
Alternatively, the second antiferromagnetic layer and the nonmagnetic layer may be provided also on the central portion of the free magnetic layer.
Preferably, the second antiferromagnetic layer provided on the central portion of the free magnetic layer exhibits non-antiferromagnetic properties, while both end portions of the second antiferromagnetic layer exhibit antiferromagnetic properties. In this configuration, no exchange coupling magnetic field is generated between the central portion of the free magnetic layer and the central portion of the second antiferromagnetic layer. Thus, the magnetization of the central portion of the free magnetic layer cannot be firmly fixed in the track width direction. On the other hand, both end portions of the second antiferromagnetic layer and the third antiferromagnetic layer formed thereon are combined into one antiferromagnetic layer; hence, both end portions of the second antiferromagnetic layer effects order transformation by annealing in a magnetic field. An exchange coupling magnetic field of an appropriate magnitude is produced between both end portions of the second antiferromagnetic layer and both end portions of the free magnetic layer, thereby firmly fixing both end portions of the free magnetic layer in the track width direction.
Preferably, the antiferromagnetic layer formed on the central portion of the free magnetic layer has a thickness of about 50 angstroms or less. Alternatively, no antiferromagnetic layer is provided on the central portion of the free magnetic layer.
If the antiferromagnetic layer formed on the central portion of the free magnetic layer has a thickness of about 50 angstroms or less, no exchange coupling magnetic field arises between the antiferromagnetic layer and the central portion of the free magnetic layer. But even if an exchange coupling magnetic field is generated, its magnitude will be extremely small.
Preferably, the antiferromagnetic layer on the central portion of the free magnetic layer has a thickness of about 40 angstroms or less.
Preferably, the thickness of the nonmagnetic layer formed on both end portions of the free magnetic layer ranges from about 0.2 angstroms to about 3 angstroms. The presence of this thin nonmagnetic layer causes antiferromagnetic interaction to take place between the second antiferromagnetic layer and the third antiferromagnetic layers. This in turn causes the second antiferromagnetic layer and the third antiferromagnetic layers to act like a single antiferromagnetic layer, which allows the magnetization of both end portions of the free magnetic layer to be properly fixed in the track width direction.
Preferably, the nonmagnetic layer is formed from one or more elements from among Ru, Re, Pd, Os, Ir, Pt, Au, and Rh. These noble metals are resistant to oxidation, and even if these noble metal elements diffuse into an antiferromagnetic layer by annealing or heat treatment, the properties of the antiferromagnetic layer are not degraded. In comparison with an element such as Ru, conventional Ta films are undesirable because they are easily oxidized. Also, the diffusion of noble metal elements such as Ta tends to cause deterioration in the properties or functions of an antiferromagnetic layer.
According to the present invention, a noble metal such as Ru is used to ensure adequate protection against oxidation even in the case of a thin nonmagnetic layer. Thus, low-energy ion milling can be carried out, permitting efficient manufacture of magnetic detection devices with excellent adaptation to tracks narrower than those used in conventional magnetic detection devices.
Preferably, the free magnetic layer is formed from three layers. For example, the free magnetic layer three-layer structure can be CoFe/NiFe/CoFe.
In the present invention, an electrode layer may be provided on the third antiferromagnetic layer. Preferably, the electrode layer is oriented in a direction parallel to the film surfaces of the layers making up the multilayer film.
A magnetic detection device in which current flows in a direction parallel to the surfaces of the layers of the magnetic detection device is known as a current-in-the-plane (CIP) type.
Alternatively, upper electrode layers may be provided on the central portion of the multilayer film and the third antiferromagnetic layer, a lower electrode layer may be provided under the multilayer film, and current passes in a direction perpendicular to the film surfaces of the layers of the multilayer film. This type of magnetic detection device is known as a current-perpendicular-to-the-plane (CPP) type.
For the CPP type magnetic detection device, the upper electrode layers are preferably upper shielding layers formed from a magnetic material. This makes it easier to fabricate magnetic detection devices and to reduce a gap length G1, so magnetic detection devices that permit higher recording density can be manufactured.
Preferably, an insulating layer is provided between the third antiferromagnetic layer and the upper electrode layer.
Preferably, a first insulating layer is provided on the upper surface of the third antiferromagnetic layer, a second insulating layer separate from the first insulating layer is provided on an inner end surface of the third antiferromagnetic layer, and the first insulating layer and the second insulating layer lie between the third antiferromagnetic layer and the upper electrode layer. With this arrangement, it is possible to effectively prevent the current that passes from the upper electrode layer to the multilayer film from shunting to the third antiferromagnetic layer. This allows fabrication of magnetic detection devices that feature high reproduction output and narrower effective reproduction tracks, which are suited for higher recording densities.
For a CPP type magnetic detection device, the lower electrode layer is preferably a lower shielding layer formed from a magnetic material. This makes it easier to fabricate magnetic detection devices and to reduce a gap length G1, so magnetic detection devices that permit higher recording density can be manufactured.
Preferably, a protuberant portion projecting toward the multilayer film is provided at the center in the track width direction of the lower electrode layer, the upper surface of the protuberant portion is in contact with the bottom surface of the multilayer film, and an insulating layer is provided between the end portions at both sides in the track width direction of the lower electrode layer and the multilayer film. This arrangement makes it difficult for the current that runs from the lower electrode layer to the multilayer film to spread beyond a track width, so current shunt loss can be minimized. Thus, the present invention allows magnetic detection devices with higher reproduction outputs and narrower effective reproducing track widths to be fabricated.
Preferably, the upper surface of the protuberant portion is flush with the upper surfaces of the insulating layers provided on both end portions of the lower electrode layer.
Preferably, the nonmagnetic material layer is formed from a nonmagnetic electrically conductive material. A magnetic detection device having the nonmagnetic material layer made of a nonmagnetic electrically conductive material is known as a spin valve GMR magneto-resistive device (CIP-GMR or CPP-GMR).
Alternatively, the nonmagnetic material layer may be formed from an insulating material. This magnetic detection device is called a spin valve tunnel magneto-resistive device (CPP-TMR).
According to another aspect of the present invention, there is provided a manufacturing method for a magnetic detection device, including the steps of:
(a) depositing a first antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic material layer, a free magnetic layer, a second antiferromagnetic layer, and a nonmagnetic layer, these components being arranged on a substrate in this order from the bottom;
(b) carrying out a first annealing in a magnetic field to generate an exchange coupling magnetic field between the first antiferromagnetic layer and the pinned magnetic layer to fix the magnetization of the pinned magnetic layer along a height direction;
(c) forming a resist layer on a central portion of the nonmagnetic layer, and removing both end portions of the nonmagnetic layer that are not covered by the resist layer, leaving both end portions of the nonmagnetic layer partly unremoved;
(d) forming third antiferromagnetic layers on both end portions of the nonmagnetic, layer that have been left unremoved, and removing the resist layer; and
(e) carrying out a second annealing in a magnetic field to generate an exchange coupling magnetic field between both end portions of the second antiferromagnetic layer, that opposes and is located under the third antiferromagnetic layer through the intermediary of the nonmagnetic layer, and both end portions of the free magnetic layer to fix the magnetization of both end portions of the free magnetic layer in a direction crossing the direction in which the pinned magnetic layer is magnetized.
In step (a) above, the first antiferromagnetic layer up to the nonmagnetic layer are sequentially formed on the substrate. When removing both end portions of the nonmagnetic layer that are not covered by the resist layer in the step (c) above, milling control is conducted to leave behind a part of both end portions of the nonmagnetic layer. Leaving a part of both end portions of the nonmagnetic layer allows the second antiferromagnetic layer formed thereunder to be protected from damage caused by ion milling. Moreover, both end portions of the nonmagnetic layer are shallowly trimmed thereby to form the third antiferromagnetic layer formed on both end portions of the nonmagnetic layer and both end portions of the second antiferromagnetic layer into a one-piece antiferromagnetic layer. Thus, the magnetization of both end portions of the free magnetic layer can be properly fixed in the track width direction by the exchange coupling magnetic field generated between both end portions of the free magnetic layer and both end portions of the second antiferromagnetic layer. On the other hand, the magnetization of the central portion of the free magnetic layer is not fixed in the track width direction as firmly as the magnetization of the end portions on both sides. This causes the central portion of the free magnetic layer to be loosely magnetized to a level that permits inverted magnetization in response to an external magnetic field.
With this arrangement, the free magnetic layer can be protected from damage due to ion milling overcutting, which has been a problem in the art, and both end portions of the free magnetic layer can be firmly fixed. In addition, the magnetization of the central portion of the free magnetic layer can be controlled to a level that allows the magnetization to be inverted in response to an external magnetic field. Hence, the present invention allows the magnetization of the free magnetic layer to be effectively controlled.
Hence, the present invention makes it possible to manufacture magnetic detection devices featuring high reproduction sensitivity and excellent reproducing characteristics even with narrower tracks.
Alternatively, both end portions of the nonmagnetic layer that are not covered by the resist layer may be completely removed to expose the surfaces of both end portions of the second antiferromagnetic layer in step (c) above, and
the third antiferromagnetic layer may be formed on the exposed second antiferromagnetic layer in the foregoing step (d).
In step (a) above, the second antiferromagnetic layer is preferably formed to have a thickness in the range of about 10 angstroms to about 50 angstroms, and more preferably from about 30 angstroms to about 40 angstroms.
In the present invention, the second antiferromagnetic layer should not be excessively thick. If the second antiferromagnetic layer is excessively thick, then order transformation easily takes place by annealing in a magnetic field, and a large exchange coupling magnetic field is apt to be generated between the central portion of the free magnetic layer and the central portion of the second antiferromagnetic layer.
Accordingly, the present invention controls the thickness of the second antiferromagnetic layer to within the range mentioned above to prevent a large exchange coupling magnetic field from being produced between the central portion of the second antiferromagnetic layer and the central portion of the free magnetic layer.
Preferably, the nonmagnetic layer has a thickness in the range of about 3 angstroms to about 10 angstroms in step (a) above. The limited thickness range permits easy adjustment of the film thickness by trimming the nonmagnetic layer by low-energy ion milling in step (c) above. The limited thickness range also ensures protection of the second antiferromagnetic layer under the nonmagnetic layer from damage due to ion milling.
Preferably, in the foregoing step (c), both end portions of the nonmagnetic layer are etched away until the thickness of both end portions of the nonmagnetic layer reaches about 3 angstroms or less, or the entire nonmagnetic layer is removed in step (c) above. This causes an antiferromagnetic interaction between the third antiferromagnetic layer from step (d) above and the second antiferromagnetic layer to form them as if they were a single antiferromagnetic layer. This particular antiferromagnetic interaction allows the magnetization of both end portions of the free magnetic layer to be properly fixed along the track width direction. It also limits the damage to the second antiferromagnetic layer under the nonmagnetic layer caused by ion milling.
Alternatively, the substrate in step (a) above may be a lower electrode layer, an insulating layer may be formed on the third antiferromagnetic layer in the foregoing step (d), and an upper electrode layer may be formed onto the insulating layer and further to the central portion of the nonmagnetic layer between the foregoing steps (d) and (e). In this case, the magnetic detection device is of the CPP type. The presence of the insulating layer between the upper electrode layer and the third antiferromagnetic layer makes it possible to effectively prevent the current passing from the upper electrode layer to the multilayer film from shunting to the third antiferromagnetic layer. This makes it possible to fabricate magnetic detection devices that feature high reproduction output and narrower effective reproduction tracks, which are suited for higher recording densities.
According to still another aspect of the present invention, there is provided a manufacturing method for a magnetic detection device including the steps of:
(f) depositing a first antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic material layer, a free magnetic layer, a second antiferromagnetic layer, and a nonmagnetic layer, these components being arranged on a substrate in this order from the bottom;
(g) carrying out a first annealing in a magnetic field to generate an exchange coupling magnetic field between the first antiferromagnetic layer and the pinned magnetic layer to fix the magnetization of the pinned magnetic layer along a height direction;
(h) removing a part of the front surface of the nonmagnetic layer;
(i) forming a third antiferromagnetic layer on the nonmagnetic layer;
(j) forming a mask layer on end portions on both sides of the third antiferromagnetic layer, and etching away the central portion of the third antiferromagnetic layer not covered by the mask layer;
(k) carrying out a second annealing in a magnetic field to generate an exchange coupling magnetic field between both end portions of the second antiferromagnetic layer under the third antiferromagnetic layer that are left under the mask layer and both end portions of the free magnetic layer to fix the magnetization of both end portions of the free magnetic layer in a direction crossing the pinned magnetic layer magnetization direction.
In step (f) above, the first antiferromagnetic layer through the nonmagnetic layer are formed in succession on the substrate. Leaving a part of the nonmagnetic layer in step (h) allows the second antiferromagnetic layer formed thereunder to be protected from damage caused by ion milling. Further, the nonmagnetic layer is shallowly etched away to allow an antiferromagnetic interaction between the third antiferromagnetic layer formed on the nonmagnetic layer and the second antiferromagnetic layer under the nonmagnetic layer, which permits the second antiferromagnetic layer and the third antiferromagnetic layer to act like a one-piece antiferromagnetic layer.
In step (j) above, the third antiferromagnetic layer at its central portion not covered by the mask layer is etched away, and the thick antiferromagnetic layer composed of the second antiferromagnetic layer and the third antiferromagnetic layers is left on both end portions of the free magnetic layer. With this arrangement, the magnetization of both end portions of the free magnetic layer can be properly fixed in the track width direction by the exchange coupling magnetic field generated between both end portions of the free magnetic layer and the second antiferromagnetic layer. On the other hand, the magnetization of the central portion of the free magnetic layer is not firmly fixed along the track width direction, so the central portion of the free-magnetic layer is weakly magnetized to a level that permits inverted magnetization in response to an external magnetic field.
With this arrangement, the free magnetic layer can be protected from damage due to ion milling overcutting, which has been a problem in the art, and both end portions of the free magnetic layer can be provided with a sufficient longitudinal bias magnetic field. Thus, the magnetization of the free magnetic layer can be properly controlled.
Hence, the present invention makes it possible to manufacture magnetic detection devices featuring high reproduction sensitivity and excellent reproducing characteristics even with narrow tracks.
In step (f) above, the second antiferromagnetic layer preferably has a thickness in the range of about 10 angstroms to about 50 angstroms, more preferably from about 30 angstroms to about 40 angstroms. This makes it difficult for the central portion of the second antiferromagnetic layer to develop order transformation by annealing in a magnetic field, so the occurrence of an exchange coupling magnetic field between the central portion of the second antiferromagnetic layer and the central portion of the free magnetic layer can be effectively prevented. Thus, the central portion of the free magnetic layer is formed into a weak single domain so it permits proper inverted magnetization in response to an external magnetic field.
Preferably, the nonmagnetic layer is formed to have a thickness in the range of about 3 angstroms to about 10 angstroms in step (f) above. The limited thickness range permits easy adjustment of the film thickness by trimming the nonmagnetic layer by low-energy ion milling in step (h) above. The limited thickness range also ensures the protection of the second antiferromagnetic layer under the nonmagnetic layer from damage caused by ion milling.
Preferably, the nonmagnetic layer left behind in step (h) above has a thickness that ranges from about 0.2 angstroms to about 3 angstroms. This allows antiferromagnetic interaction between the third antiferromagnetic layer left on both end portions of the free magnetic layer and the second antiferromagnetic layer, so the third antiferromagnetic layer and the second antiferromagnetic layer act like a one-piece antiferromagnetic layer. Thus, the magnetization of both end portions of the free magnetic layer can be properly fixed in the track width direction.
Alternatively, in step (j) above, the third antiferromagnetic layer not covered by the mask layer may be completely removed to expose the front surface of the nonmagnetic layer.
Alternatively, in step (j) above, the third antiferromagnetic layer not covered by the mask layer may be entirely removed, and the exposed nonmagnetic layer may also be entirely removed to expose the front surface of the second antiferromagnetic layer.
Alternatively, the second annealing in a magnetic field in step (k) above may be carried out after step (i) and before step (j).
Alternatively, the substrate in step (f) may be a lower electrode layer,
the first insulating layer may be formed on the third antiferromagnetic layer in step (i),
the mask layer may be formed on both end portions of the first insulating layer, and the central portions of the first insulating layer and the third antiferromagnetic layer that are not covered by the mask layer may be etched away in step (j),
the second insulating layer may be formed onto the first insulating layer, inner end surfaces of the third antiferromagnetic layers, and the central portion sandwiched by the third antiferromagnetic layers. Then, the second insulating layer may be removed, leaving a part of the second insulating layer formed on the inner end surfaces of the third antiferromagnetic layers, after step (j), and
the upper electrode layer may be formed onto the first insulating layer to the second insulating layer and the central portion.
In this case, the magnetic detection device is the CPP type. The presence of the first insulating layer and the second insulating layer between the upper electrode layer and the third antiferromagnetic layer makes it possible to prevent the current passing from the upper electrode layer to the multilayer film from shunting to the third antiferromagnetic layer. This makes it possible to fabricate magnetic detection devices that feature high reproduction output and narrower effective reproduction tracks, which are suited for higher recording densities.
Alternatively, in place of step (i), the first insulating layer may be formed on both end portions of the third antiferromagnetic layer, and
in place of step (j), the central portion of the third antiferromagnetic layer that is not covered by the first insulating layer may be etched away using the first insulating layer as a mask.
Preferably, the angle for forming the second insulating layer is set to an angle xcex81 with respect to the plane perpendicular to the surface of the lower electrode layer, and the incident angle for trimming the second insulating layer is set to an angle xcex82, which is smaller than the angle xcex81.
The second insulating layer is preferably etched away in a perpendicular direction or a direction close to the perpendicular direction. This makes it easier to partly leave the second antiferromagnetic layer on the inner end surface of the third antiferromagnetic layer. This also properly etches away the second insulating layer or the like which is formed on the central portion of the third antiferromagnetic layer.
Thus, it is possible to easily manufacture a CPP type magnetic detection device in which current properly passes from the upper electrode layer into the multilayer film, and the current does not shunt to the third antiferromagnetic layer.
Alternatively, both end portions of the lower electrode layer may be etched away to form an insulating layer on the end portions on both sides. The first antiferromagnetic layer may be formed on the protuberant portion formed on the central portion of the lower electrode layer, and on the insulating layer.
Alternatively, the lower electrode layer and the upper electrode layer may be formed from a magnetic material.
Preferably, the nonmagnetic layer is formed from one or more elements that include Ru, Re, Pd, Os, Ir, Pt, Au, and Rh. These noble metals are resistant to oxidation, so an increase in film thickness due to oxidation can be prevented, in contrast to Ta films. Moreover, even when these noble metal elements diffuse into an antiferromagnetic layer by annealing or heat treatment, the antiferromagnetic layer properties are not degraded. In comparison with Ru or the like, conventional Ta films are undesirable because they tend to degrade the properties or functions of the antiferromagnetic layer if they diffuse into the antiferromagnetic layer.
According to the present invention, a noble metal such as Ru is used in place of Ta to permit the adjustment of the thickness of the nonmagnetic layer formed from Ru or the like by low-energy ion milling. In addition, the second antiferromagnetic layer formed under the nonmagnetic layer can be properly protected from damage caused by ion milling. Further, and the second and third antiferromagnetic layers on both end portions of the free magnetic layer can function like a one-piece antiferromagnetic layer through the nonmagnetic layer. This arrangement permits the magnetization of both end portions of the free magnetic layer to be fixed more effectively along the track width direction.
Preferably, the free magnetic layer is formed using a three-layer structure in step (a) or (f). In particular, the free magnetic layer preferably has a CoFe/NiFe/CoFe three-layer structure.